This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The pilot study will assess the dopaminergic effects of branched-chain amino acids (BCAA) in ten 18-40 year old male healthy subjects. The effects on dopamine activity will be measured with plasma catecholamine and prolactin levels, and dopamine D2 receptor availability (assessed with [11C]-raclopride and positron emission tomography following the oral administration of a BCAA mixture).